1. Field of the Invention
This invention is utilized in devices which convert mechanical energy produced during braking of an internal combustion engine into electrical energy, store this electrical energy, and supply stored electrical energy to an auxiliary acceleration device when the internal combustion engine is to be accelerated, thereby generating mechanical energy. In particular, this invention is utilized in devices in which a rotary squirrel-cage polyphase induction machine is coupled to a rotary shaft of an internal combustion engine, and in which this squirrel-cage polyphase induction machine acts as an electric generator during braking and as an electric motor during acceleration. This invention is a device which is suited to being carried by a motor vehicle equipped with an auxiliary acceleration and auxiliary braking device.
2. Description of the Related Art
The present applicant has disclosed an electric braking and auxiliary acceleration means for motor vehicles in PCT Publication No. WO88/O6107 (PCT Application No. PCT/JP88/00157). As shown in FIG. 12, this device is equipped with a squirrel-cage polyphase induction machine 2, the rotor of which is directly connected to internal combustion engine 1; storage battery circuit 3 for storing electricity; inverter circuit 4 which converts the DC voltage of this storage battery circuit 3 to an AC voltage of a frequency suitable for inducing a rotating magnetic field with a lower rotational speed than the axial rotational speed of squirrel-cage polyphase induction machine 2, and which gives this AC voltage to squirrel-cage polyphase induction machine 2, and which converts AC power from squirrel-cage polyphase induction machine 2 to DC power; and inverter control circuit 5 which generates control signals which set the frequency of the AC-side voltage of this inverter circuit 4. This inverter control circuit 5 includes means for generating control commands from the driver to suit the operation of the motor vehicle.
Squirrel-cage polyphase induction machine 2 is also fitted with rotation sensor 6, and signals from this rotation sensor 6 are given to inverter control circuit 5, to which information from storage battery circuit 3 relating to the charge condition of the storage battery is also input.
Capacitor 7 and semiconductor switching circuit 12 are connected to the output of inverter circuit 4. Resistor 11 is also connected to the output of inverter circuit 4, via this semiconductor switching circuit 12. Resistor 11 is constituted in a manner such that it dissipates any excess electrical energy which is generated by heavy braking of the vehicle and which cannot be regenerated.
Detection circuit 13 for detecting the output voltage of inverter circuit 4 is also connected to storage battery circuit 3 and semiconductor switching circuit 12, and current detector 15 is provided at resistor 11 for detecting changes in current. Switching control circuit 14 is connected to current detector 15, and controls semiconductor switching circuit 12 in accordance with its detection signals. Detection circuit 13 is connected to this switching control circuit 14.
When a motor vehicle equipped with this device brakes, energy generated by braking is recovered and stored as electrical energy, and when such a vehicle accelerates, this stored electrical energy is converted to mechanical energy, thereby supplying auxiliary motive power to the internal combustion engine which drives the axle.
That is to say, the control circuit which controls the inverter does so in such a manner that in an acceleration mode, in which the squirrel-cage polyphase induction machine is used as an auxiliary driving means for the internal combustion engine, the inverter circuit provides the squirrel-cage polyphase induction machine with a rotating magnetic field which has a rotational speed that exceeds the rotational speed of the internal combustion engine; while in deceleration mode, in which the squirrel-cage polyphase induction machine is used as a braking device for the internal combustion engine, the inverter circuit provides the squirrel-cage polyphase induction machine with a rotating magnetic field which has a rotational speed which is less than the rotational speed of the internal combustion engine. In the acceleration mode, the inverter circuit gives the DC output resulting from the electrical energy that has been stored in the electricity storage means to the squirrel-cage polyphase induction machine as a polyphase AC output; while in deceleration mode, it gives the polyphase AC output energy of the squirrel-cage polyphase induction machine to the electricity storage means as a DC output.
In this previous device, the aforementioned electricity storage means is a storage battery. That is to say, the rated voltage at the DC side of the inverter is 200.about.300 V, and a storage battery with this rated voltage is obtained by connecting a large number of motor vehicle lead storage batteries in series.
The applicant has successfully designed and manufactured practical versions of the aforementioned device and has introduced them on a trial basis, mainly in buses making regular runs in urban areas. It has therefore been possible to carry out numerous tests.
The results of these tests have indicated that the device described above is an extremely useful device which does not simply dissipate the energy generated during braking but is able to recover and utilize it effectively. The results have also shown that this device gives an essentially excellent performance which enables it to be implemented not just in large motor vehicles, but also more widely in passenger cars and small goods vehicles as well. However, it was found that the following problems arise when a large lead storage battery is carried on a practical vehicle:
A considerable volume is taken up . . . more specifically, because ten or more series-connected 24 V lead storage batteries are used, the total volume is 0.2.about.0.4 m.sup.2. PA0 Vehicle body weight increases . . . more specifically, there is an increase of 200.about.300 kg. PA0 There must be a mounting structure that will provide adequate safety for human beings, given that DC electric power of several tens of amperes at voltages in excess of 200 V will be utilized . . . more specifically, it is necessary to have a safe arrangement of the sort where dangerous electrical parts are mounted in a secure box provided with a door that can be opened and shut, and where the circuits are automatically isolated when the door is opened. PA0 Because lead storage batteries are devices that involve chemical reactions, various maintenance procedures are required. For example, the amount of electrolyte has to be observed under fixed conditions and its specific gravity measured, the electrolyte has to be replenished, and supplementary charging carried out . . . the man-hours involved in such maintenance become considerable, and its application to private automobiles is difficult. PA0 To give convenient maintenance, all the batteries have to be arranged in one place . . . sufficient space for this cannot be found in a small vehicle. PA0 There are energy losses due to the internal resistance of the cells . . . this impairs the efficiency with which energy recovered during braking is utilized during acceleration. PA0 Under ordinary operating conditions, the present storage capacity of the batteries cannot be detected electrically accurately enough for use in automatic control . . . although the present storage capacity can be found fairly accurately by measuring the specific gravity of the electrolyte, sufficient accuracy cannot be guaranteed in measurements with simple ammeters or voltmeters, due to the aforementioned internal resistance changing with change in temperature, so electrical ,measurements cannot be utilized as real-time control information. PA0 an initial charging mode wherein, with the internal combustion engine at a standstill, the aforementioned electrostatic capacitive circuit is charged with the energy of the aforementioned storage battery after the voltage has been stepped up by the step-up/step-down converter; PA0 a starting mode wherein, when the internal combustion engine is being started, energy stored in the electrostatic capacitive circuit is given to the aforementioned squirrel-cage polyphase induction machine as an AC current via the aforementioned inverter circuit, and the squirrel-cage polyphase induction machine is made to operate as an electric motor; PA0 a deceleration mode wherein, when the vehicle is being braked, the squirrel-cage polyphase induction machine is made to operate as an electric generator, and the output AC current of the squirrel-cage polyphase induction machine is supplied to the aforementioned electrostatic capacitive circuit as a charging current via the aforementioned inverter circuit; and PA0 an acceleration mode wherein, when the vehicle is being accelerated, the squirrel-cage polyphase induction machine is made to operate as an electric motor, and energy stored in the electrostatic capacitive circuit is supplied via the inverter circuit to the squirrel-cage polyphase induction machine as an AC current. PA0 a warm-up mode wherein, when the internal combustion engine is warming up, the squirrel-cage polyphase induction machine is made to operate as an electric generator, and the output AC current of said squirrel-cage polyphase induction machine is supplied via the inverter circuit to the electrostatic capacitive circuit as a charging current; and PA0 a supplementary charging mode wherein, when the internal combustion engine is operating and the terminal voltage of the aforementioned electrostatic capacitive circuit has fallen to or below a prescribed value, the squirrel-cage polyphase induction machine is made to operate as an electric generator, and the output AC current of said squirrel-cage polyphase induction machine is supplied via the inverter circuit to the electrostatic capacitive circuit as a charging current. PA0 an initial charging mode, wherein the electrostatic capacitive circuit is charged with the energy of the storage battery after conversion by the aforementioned DC-to-DC converter; and PA0 a battery charging mode, wherein, when the terminal voltage of the electrostatic capacitive circuit exceeds a prescribed value, the storage battery is charged with the stored electrical energy of this electrostatic capacitive circuit after conversion by the DC-to-DC converter.
The present invention is proposed as a means of solving the aforementioned problems. In other words, the object of this invention is to provide a device which solves the various problems described above and which enables the above described principle of good energy utilization efficiency to be widely implemented, even in smaller motor vehicles.